Interferon-gamma arrests proliferation and causes apoptosis in stromal cell/interleukin-7-dependent normal murine pre-B cell lines and clones in vitro, but does not induce differentiation to surface immunoglobulin-positive B cells

Cell circuits and niches controlling B cell development

Studies over the last decade uncovered overlapping niches for hematopoietic stem cells (HSCs), multipotent progenitor cells, common lymphoid progenitors, and early B cell progenitors. HSC and lymphoid niches are predominantly composed by mesenchymal progenitor cells (MPCs) and by a small subset of endothelial cells. Niche cells create specialized microenvironments through the concomitant production of short-range acting cell-fate determining cytokines such as interleukin (IL)-7 and stem cell factor and the potent chemoattractant C-X-C motif chemokine ligand 12. This type of cellular organization allows for the cross-talk between hematopoietic stem and progenitor cells with niche cells, such that niche cell activity can be regulated by the quality and quantity of hematopoietic progenitors being produced. For example, preleukemic B cell progenitors and preB acute lymphoblastic leukemias interact directly with MPCs, and downregulate IL-7 expression and the production of non-leukemic lymphoid cells. In this review, we discuss a novel model of B cell development that is centered on cellular circuits formed between B cell progenitors and lymphopoietic niches.

Foxp3+ regulatory T cells ensure B lymphopoiesis by inhibiting the granulopoietic activity of effector T cells in mouse bone marrow

Foxp3(+) Treg cells are crucial for maintaining T-cell homeostasis, but their role in B-cell homeostasis remains unclear. Here, we found that Foxp3 mutant scurfy mice had fewer B-lineage cells and progenitors, including common lymphoid progenitors and lymphoid-primed multipotent progenitors, but higher myeloid-lineage cell numbers in BM compared with WT littermates. Homeostasis within the HSC compartment was also compromised with apparent expansion of long- and short-term HSCs. This abnormality was due to the lack of Treg cells, but not to the Treg-cell extrinsic functions of Foxp3 or cell-autonomous defects. Among cytokines enriched in the BM of scurfy mice, IFN-γ affected only B lymphopoiesis, but GM-CSF, TNF, and IL-6 collectively promoted granulopoiesis at the expense of B lymphopoiesis. Neutralization of these three cytokines reversed the hematopoietic defects on early B-cell progenitors in scurfy mice. Treg cells ensured B lymphopoiesis by reducing the production of these cytokines by effector T cells, but not by directly affecting B lymphopoiesis. These results suggest that Treg cells occupy an important niche in the BM to protect B-lineage progenitor cells from excessive exposure to a lymphopoiesis-regulating milieu.

Impact of interferon-γ on hematopoiesis

The proinflammatory cytokine interferon-γ (IFN-γ) is well known for its important role in innate and adaptive immunity against intracellular infections and for tumor control. Yet, it has become clear that IFN-γ also has a strong impact on bone marrow (BM) output during inflammation, as it affects the differentiation of most hematopoietic progenitor cells. Here, we review the impact of IFN-γ on hematopoiesis, including the function of hematopoietic stem cells (HSCs) and more downstream progenitors. We discuss which hematopoietic lineages are functionally modulated by IFN-γ and through which underlying molecular mechanism(s). We propose the novel concept that IFN-γ acts through upregulation of suppressor of cytokine signaling molecules, which impairs signaling of several cytokine receptors. IFN-γ has also gained clinical interest from different angles, and we discuss how chronic IFN-γ production can lead to the development of anemia and BM failure and how it is involved in malignant hematopoiesis. Overall, this review illustrates the wide-ranging effect of IFN-γ on the (patho-)physiological processes in the BM.

Severe Developmental B Lymphopoietic Defects in Foxp3-Deficient Mice are Refractory to Adoptive Regulatory T Cell Therapy

The role of Foxp3-expressing regulatory T (T_reg) cells in tolerance and autoimmunity is well-established. However, although of considerable clinical interest, the role of T_reg cells in the regulation of hematopoietic homeostasis remains poorly understood. Thus, we analysed B and T lymphopoiesis in the scurfy (Sf) mouse model of T_reg cell deficiency. In these experiments, the near-complete block of B lymphopoiesis in the BM of adolescent Sf mice was attributed to autoimmune T cells. We could exclude a constitutive lympho-hematopoietic defect or a B cell-intrinsic function of Foxp3. Efficient B cell development in the BM early in ontogeny and pronounced extramedullary B lymphopoietic activity resulted in a peripheral pool of mature B cells in adolescent Sf mice. However, marginal zone B and B-1a cells were absent throughout ontogeny. Developmental B lymphopoietic defects largely correlated with defective thymopoiesis. Importantly, neonatal adoptive T_reg cell therapy suppressed exacerbated production of inflammatory cytokines and restored thymopoiesis but was ineffective in recovering defective B lymphopoiesis, probably due to a failure to compensate production of stroma cell-derived IL-7 and CXCL12. Our observations on autoimmune-mediated incapacitation of the BM environment in Foxp3-deficient mice will have direct implications for the rational design of BM transplantation protocols for patients with severe genetic deficiencies in functional Foxp3⁺ T_reg cells.

The many roles of IL-7 in B cell development; mediator of survival, proliferation and differentiation

Interleukin-7 (IL-7) plays several important roles during B cell development including aiding in; the specification and commitment of cells to the B lineage, the proliferation and survival of B cell progenitors; and maturation during the pro-B to pre-B cell transition. Regulation and modulation of IL-7 receptor (IL-7R) signaling is critical during B lymphopoiesis, because excessive or deficient IL-7R signaling leads to abnormal or inhibited B cell development. IL-7 works together with E2A, EBF, Pax-5 and other transcription factors to regulate B cell commitment, while also functions to regulate Ig rearrangement by modulating FoxO protein activation and Rag enhancer activity. Suppressor of cytokine signaling (SOCS) proteins are inhibitors of cytokine activation and, in B cells, function to fine tune IL-7R signaling; ensuring that appropriate IL-7 signals are transmitted to allow for efficient B cell commitment and development.

Autoimmune bone marrow environment severely inhibits B cell development by inducing extensive cell death and inhibiting proliferation

The spontaneous scurfy (sf) mutation in mice results in a complete loss of Tregs, leading to a lethal, multi-system autoimmune syndrome. We have carefully examined B lymphopoiesis in sf mice. Paradoxically, the B cell numbers at all developmental stages including pro-B, pre-B, immature and mature B cells are significantly decreased in the BM and spleen of sf mice, compared to that of wild-type littermate controls. The developing B cells in sf mice exhibit profoundly elevated cell death induced by down-regulation of Bcl-XL expression and up-regulation of Fas expression. In addition, the clonal expansion of pre-B and immature B cells in sf mice is significantly reduced compared to wild-type controls. Foxp3 expression is not detectable in all stages of developing B cells in wild-type mice, indicating that the defects are B-cell extrinsic, which is further supported by the recovery of B cell maturation in BM chimeric mice. Remarkably, IFN-γ production is significantly elevated in numerous cell types in the BM of sf mice. Taken together, these results indicate that the autoimmune inflammatory marrow environment has dramatic inhibitory effects on B cell development by inducing apoptosis and suppressing proliferation of developing B cells.

The in vitro derivation of phenotypically mature and diverse B cells from immature spleen and bone marrow precursors

The capacity of immature B cells of the spleen and bone marrow to differentiate in vitro into cells representing mature end stage cells was investigated using B-cell activating factor belonging to the TNF family (BAFF) and Notch pathway activators. Immature splenic and bone marrow B cells were found, in the presence of both of these activators, to mature into cells with follicular mature (FM) and marginal zone (MZ) cell phenotypes. Such cells were functionally responsive to B-cell-specific activation. The derivation in vitro of cells with an MZ phenotype was more robust from CD23(-) populations than CD23(+) immature/transitional B cells, suggesting a direct immature/T1 B cell to MZ cell differentiation pathway. Transcript analysis of the in vitro-derived B-cell populations demonstrated expression profiles similar to maturing B cells in vivo. FACS-purified populations of B220(+)CD19(+)CD21(-)CD23(-) cells from bone marrow of 2-wk-old mice gave rise to populations of CD21(+)CD23(-) cells with MZ cell phenotypes as well as CD21(+)CD23(+) cells with FM cell phenotypes in percentages similar to those found in vivo. These data suggest that the commitment to an MZ and FM B cell phenotype is set prior to immature B-cell release from the marrow.

Hypercostimulation through 4-1BB distorts homeostasis of immune cells

The deleterious side effects associated with a recent clinical trial with anti-CD28 superagonist Abs have questioned the use of reagents to costimulatory molecules in human therapy. We now show that sustained signaling from an agonist Ab to 4-1BB, a member of the TNFR superfamily, results in detrimental effects on immune cell homeostasis. Repeated anti-4-1BB treatment during the reconstitution of hematopoietic cells in irradiated mice engrafted with bone marrow, or in mice infected with vaccinia virus, induced abnormal apoptosis of premature and immature B cells in the bone marrow, and led to peripheral B cell depletion. Inhibition of B cell development was indirect and due to costimulation of CD8 T cells and dependent on IFN-gamma. Moreover, anti-4-1BB also suppressed the development of NK and NKT cells, but in this case independently of T cells and IFN-gamma. The altered NK cell homeostasis resulted from activation-induced cell death triggered by anti-4-1BB. These results show that hypercostimulation elicits strong T cell immunity, but it can simultaneously distort immune homeostasis, suggesting that careful attention to activity, dose, and periodicity of treatment will be needed in any immunotherapeutic strategy with agonist Abs to costimulatory molecules.

JunB is a gatekeeper for B-lymphoid leukemia

Loss of JunB has been observed in human leukemia and lymphoma, but it remains unknown, whether this loss is relevant to disease progression. Here, we investigated the consequences of JunB deficiency using Abelson-induced B-lymphoid leukemia as a model system. Mice deficient in JunB expression succumbed to Abelson-induced leukemia with increased incidence and significantly reduced latency. Similarly, bcr/abl p185-transformed JunB-deficient (junB(Delta/Delta)) cells induced leukemia in RAG2(-/-) mice displaying a more malignant phenotype. These observations indicated that cell intrinsic effects within the junB(Delta/Delta) tumor cells accounted for the accelerated leukemia development. Indeed, explantated bcr/abl p185 transformed junB(Delta/Delta) cells proliferated faster than the control cells. The proliferative advantage emerged slowly after the initial transformation process and was associated with increased expression levels of the cell cycle kinase cdk6 and with decreased levels of the cell cycle inhibitor p16(INK4a). These alterations were due to irreversible reprogramming of the cell, because - once established - accelerated disease induced by junB(Delta/Delta) cells was not reverted by re-introducing JunB. Consistent with this observation, we found that the p16 promoter was methylated. Thus, JunB functions as a gatekeeper during tumor evolution. In its absence, transformed leukemic cells acquire an enhanced proliferative capacity, which presages a more malignant disease.

TC-PTP-deficient bone marrow stromal cells fail to support normal B lymphopoiesis due to abnormal secretion of interferon-{gamma}

The T-cell protein tyrosine phosphatase (TC-PTP) is a negative regulator of the Jak/Stat cytokine signaling pathway. Our study shows that the absence of TC-PTP leads to an early bone marrow B-cell deficiency characterized by hindered transition from the pre-B cell to immature B-cell stage. This phenotype is intrinsic to the B cells but most importantly due to bone marrow stroma abnormalities. We found that bone marrow stromal cells from TC-PTP(-/-) mice have the unique property of secreting 232-890 pg/mL IFN-gamma. These high levels of IFN-gamma result in 2-fold reduction in mitotic index on IL-7 stimulation of TC-PTP(-/-) pre-B cells and lower responsiveness of IL-7 receptor downstream Jak/Stat signaling molecules. Moreover, we noted constitutive phosphorylation of Stat1 in those pre-B cells and demonstrated that this was due to soluble IFN-gamma secreted by TC-PTP(-/-) bone marrow stromal cells. Interestingly, culturing murine early pre-B leukemic cells within a TC-PTP-deficient bone marrow stroma environment leads to a 40% increase in apoptosis in these malignant cells. Our results unraveled a new role for TC-PTP in normal B lymphopoiesis and suggest that modulation of bone marrow microenvironment is a potential therapeutic approach for selected B-cell leukemia.

Effects of interferon gamma on native human acute myelogenous leukaemia cells

T cell targeting immunotherapy is now considered a possible strategy in acute myelogenous leukaemia (AML), and IFNgamma release may then contribute to the antileukaemic effects. We investigated the effects of IFNgamma on native human AML cells. Normal T cells could be activated to release IFNgamma in the presence of AML cells. Furthermore, high levels of CD119 (IFNgamma receptor alpha chain) expression were observed for all 39 patients examined. Receptor expression was decreased after exposure to exogenous IFNgamma, and receptor ligation caused Stat1 phosphorylation but no phosphorylation of the alternative messengers Erk1/2. The effect of exogenous IFNgamma on AML blast proliferation was dependent on the local cytokine network and IFNgamma (1) inhibited proliferation in the presence of exogenous IL1beta, GM-CSF, G-CSF and SCF; (2) had divergent effects in the presence of IL3 and Flt3 (65 patients examined); (3) inhibited proliferation in the presence of endothelial cells but had divergent effects in the presence of fibroblasts, osteoblasts and normal stromal cells (65 patients examined). IFNgamma increased stress-induced (spontaneous) in vitro apoptosis as well as cytarabine-induced apoptosis only for a subset of patients. Furthermore, IFNgamma decreased the release of proangiogenic CXCL8 and increased the release of antiangiogenic CXCL9-11. We conclude that IFNgamma can be released in the presence of native human AML cells and affect AML cell proliferation, regulation of apoptosis and the balance between pro- and antiangiogenic chemokine release.

Annexin V associates with the IFN-gamma receptor and regulates IFN-gamma signaling

Many of the biological activities of IFN-gamma are mediated through the IFN-gammaR3-linked Jak-Stat1alpha pathway. However, regulation of IFN-gamma signaling is not fully understood, and not all responses to IFN-gamma are Stat1alpha dependent. To identify novel elements involved in IFN-gamma cell regulation, the cytoplasmic domain of the R2 subunit of the human IFN-gammaR was used as bait in a yeast two-hybrid screen of a human monocyte cDNA library. This identified annexin A5 (AxV) as a putative IFN-gammaR binding protein. The interaction was confirmed in pull-down experiments in which a GST-R2 cytoplasmic domain fusion protein was incubated with macrophage lysates. Furthermore, immunoprecipitation using anti-IFN-gammaR2 Abs showed that AxV interacted with IFN-gammaR2 to form a stable complex following incubation of cells with IFN-gamma. In 293T cells with reduced expression of AxV, brought about by small interfering RNA targeting, activation of Jak2 and Stat1alpha in response to IFN-gamma was enhanced. Inhibition of cell proliferation, a hallmark of the IFN-gamma response, also was potentiated in HeLa cells treated with small interfering RNA directed at AxV. Taken together, these results suggest that through an inducible association with the R2 subunit of the IFN-gammaR, AxV modulates cellular responses to IFN-gamma by modulating signaling through the Jak-Stat1 pathway.

Identification of the nonreceptor tyrosine kinase MATK/CHK as an essential regulator of immune cells using Matk/CHK-deficient mice

Matk/CHK knockout mice were reported to show no apparent phenotypic abnormalities. This was thought to be due to the homologous kinase Csk that compensates for Matk/CHK. Here, we present the first evidence that the nonreceptor tyrosine kinase, Matk/CHK, is an important modulator of immune cell signaling. We found that the frequency of primitive hematopoietic cells, the side population c-kit(+) Lin(-) Sca-1(+) (SPKLS) cells, in Matk/CHK(-/-) mice was increased 2.2-fold compared with the control mice. Moreover, Matk/CHK deficiency led to significantly higher pre-B cell colony formation following IL-7 stimulation. Interestingly, when mice received the in vivo antigen challenge of TNP-ovalbumin followed by restimulation, the Matk/CHK(-/-) lymph node and spleen cells produced significantly lower IFN-gamma levels compared with the respective wild-type cells. Our study indicates that Matk/CHK is not functionally redundant with Csk, and that this tyrosine kinase plays an important role as a regulator of immunologic responses.

The role of suppressors of cytokine signaling (SOCS) proteins in regulation of the immune response

Cytokines are an integral component of the adaptive and innate immune responses. The signaling pathways triggered by the engagement of cytokines with their specific cell surface receptors have been extensively studied and have provided a profound understanding of the intracellular machinery that translates exposure of cells to cytokine to a coordinated biological response. It has also become clear that cells have evolved sophisticated mechanisms to prevent excessive responses to cytokines. In this review we focus on the suppressors of cytokine signaling (SOCS) family of cytoplasmic proteins that completes a negative feedback loop to attenuate signal transduction from cytokines that act through the janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway. SOCS proteins inhibit components of the cytokine signaling cascade via direct binding or by preventing access to the signaling complex. The SOCS proteins also appear to target signal transducers for proteasomal destruction. Analyses of genetically modified mice in which SOCS proteins are overexpressed or deleted have established that this family of negative regulators has indispensable roles in regulating cytokine responses in cells of the immune system as well as other tissues. Emerging evidence also suggests that disruption of SOCS expression or activity is associated with several immune and inflammatory diseases, raising the prospect that manipulation of SOCS activity may provide a novel future therapeutic strategy in the management of immunological disorders.

Exogenous gamma and alpha/beta interferon rescues human macrophages from cell death induced by Bacillus anthracis

During the recent bioterrorism-related outbreaks, inhalational anthrax had a 45% mortality in spite of appropriate antimicrobial therapy, underscoring the need for better adjuvant therapies. The variable latency between exposure and development of disease suggests an important role for the host's innate immune response. Alveolar macrophages are likely the first immune cells exposed to inhalational anthrax, and the interferon (IFN) response of these cells comprises an important arm of the host innate immune response to intracellular infection with Bacillus anthracis. Furthermore, IFNs have been used as immunoadjuvants for treatment of another intracellular pathogen, Mycobacterium tuberculosis. We established a model of B. anthracis infection with the Sterne strain (34F(2)) which contains lethal toxin (LeTx). 34F(2) was lethal to murine and human macrophages. Treatment with IFNs significantly improved cell viability and reduced the number of germinated intracellular spores. Infection with 34F(2) failed to induce the latent transcription factors signal transducer and activators of transcription 1 (STAT1) and ISGF-3, which are central to the IFN response. Furthermore, 34F(2) reduced STAT1 activation in response to exogenous alpha/beta IFN, suggesting direct inhibition of IFN signaling. Even though 34F(2) has LeTx, there was no mitogen-activated protein kinase kinase 3 cleavage and p38 was normally induced, suggesting that these early effects of B. anthracis infection in macrophages are independent of LeTx. These data suggest an important role for both IFNs in the control of B. anthracis and the potential benefit of using exogenous IFN as an immunoadjuvant therapy.

STAT1-induced apoptosis is mediated by caspases 2, 3, and 7

STAT1 (signal transducer and activator of transcription 1) has been implicated as a mediator of a variety of biological responses in response to stimulation by specific growth factors and cytokines. To understand better the role of STAT1 in the interferon-gamma (IFN-gamma)-induced phenotype, we generated an active form of STAT1 (STAT1C) by substituting Cys residues for both Arg-656 and Asn-658 within the C-terminal loop of the STAT1 SH2 domain. The IFN-gamma activation site element was stimulated and bound efficiently by STAT1C without IFN-gamma treatment. STAT1C was found to be tyrosine-phosphorylated in the nucleus for more than 30 h after IFN-gamma stimulation. STAT1-negative U3A cells reexpressing STAT1C showed retarded cell growth and underwent apoptosis when treated with IFN-gamma. Further analysis demonstrated that apoptosis was preceded by proteolytic cleavage of caspases 2, 3, and 7, and wild type STAT1 also induced cleavage of caspase 7 when expressed in STAT1-negative U3A cells, indicating that STAT1C augments potential activity of wild type STAT1. Studies with cycloheximide treatment showed that protein synthesis induced in the first 24 h after IFN-gamma treatment was required for apoptosis under these conditions. Finally, we found that STAT1C-induced apoptosis was, in part, mediated by caspase 2, 3, and 7 because benzyloxycarbonyl-valyl-aspartyl-valyl-alanyl-aspartic acid fluoromethyl ketone (Z-VDVAD-FMK) treatment partially blocked apoptosis. These results suggest that prolonged nuclear localization of activated STAT1 results in apoptosis involving specific regulation of caspase pathway.

A novel instance of class I modification (cim) affecting two of three rat class I RT1-A molecules within one MHC haplotype

MHC class I expression by rats of the RT1(o), RT1(d), and RT1(m) MHC haplotypes was investigated. Identical, functional cDNAs were obtained from RT1(o) and BDIX (RT1(dv1)) rats for three MHC class I molecules. RT1-A1(o/d) and -A2(o/d) are closely related in sequence to other cloned rat class Ia genes that have been shown to map to the RT1-A region, while RT1-A3 degrees is highly homologous to a class I gene identified by sequencing an RT1-A(n) genomic contig and is named A3(n). Detailed analysis of the three molecules was undertaken using serology with mAbs, two-dimensional gel analysis of immunoprecipitates, and killing assays using cytotoxic T cells. Arguments are presented suggesting that A1 degrees is the principal MHC class Ia (classical) restricting element of this haplotype. A2 degrees, which is highly cross-reactive with A1 degrees, and A3 degrees probably play more minor or distinct roles in Ag presentation. Unexpectedly, cDNAs encoding exactly the same three molecules were cloned from rats of the RT1(m) haplotype, an MHC that until now was thought to possess unique class Ia genes. RT1(m) contains the TAP-B allele of the TAP transporter, and we present evidence that functional polymorphism in rat TAP has an even greater impact on the expression of RT1-A1 degrees and -A2 degrees than it does on RT1-A(a) in the established case of class I modification (cim). Historically, this led to the misclassification of RT1(m) class Ia molecules as separate and distinct.

Jak1 deficiency leads to enhanced Abelson-induced B-cell tumor formation

The Janus kinase Jak1 has been implicated in tumor formation by the Abelson oncogene. In this study we show that loss of Jak1 does not affect in vitro transformation by v-abl as defined by the ability to induce cytokine-independent B-cell colony formation or establishment of B-cell lines. However, Jak1-deficient, v-abl-transformed cell lines were more tumorgenic than wild-type cells when transplanted subcutaneously into severe combined immunodeficient (SCID) mice or injected intravenously into nude mice. Jak1 deficiency was associated with a loss in the ability of interferon-gamma (IFN-gamma)to induce growth arrest and/or apoptosis of v-abl-transformed pre-B cells or tumor growth in SCID mice. Moreover, IFN-gamma mRNA could be detected in growing tumors, and tumor cells explanted from SCID mice had lost the ability to respond to IFN-gamma in 9 of 20 cases, whereas the response to interferon-alpha (IFN-alpha) remained intact. Importantly, a similar increase in tumorgenicity was observed when IFN-gamma-deficient cells were injected into SCID mice, identifying the tumor cell itself as the main source of IFN-gamma. These findings demonstrate that Jak1, rather than promoting tumorgenesis as previously proposed, is critical in mediating an intrinsic IFN-gamma-dependent tumor surveillance.

The mesenchymal stroma negatively regulates B cell lymphopoiesis through the expression of activin A

The negative control of B cell generation is only partially resolved. We assessed the role of activin A in regulation of B lymphopoiesis in view of its specific inhibitory effects on tumor B lineage cells. Activin A is constitutively expressed in mouse hemopoietic organs and in cultured mesenchymal cell lines. We observed an inverse relationship between activin A titer and B lineage cell production. In the spleen, the red pulp exhibited a relatively higher abundance of the protein as compared with the lymphoid follicles, wherein B cell accumulation occurs. Furthermore, a specific shut off in activin A expression was observed in bone marrow and spleen following in vivo induction of B lymphocyte polyclonal activation. We further substantiated these in vivo observations by in vitro studies of primary bone marrow cultures, in which the expression of functional activin A was found to be diminished prior to the onset of B lymphopoiesis. The reduction in functional activin A is shown to concomitantly occur with spontaneous induction of the expression of activin A specific inhibitors. We therefore propose that the mesenchymal organ stroma expresses activin A that negatively controls B cell lymphopoiesis.

Gamma interferon inhibits production of Anti-OspA borreliacidal antibody in vitro

The ability of a Lyme borreliosis vaccine to induce and maintain sustained levels of borreliacidal antibody is necessary for prolonged protection against infection with Borrelia burgdorferi. Vaccination against infection with B. burgdorferi could be improved by determining the mechanism(s) that influences the production of protective borreliacidal antibody. Borreliacidal antibody was inhibited in cultures of lymph node cells obtained from C3H/HeJ mice vaccinated with formalin-inactivated B. burgdorferi and cultured with macrophages and B. burgdorferi and treated with recombinant gamma interferon (rIFN-gamma). The suppression of production of outer surface protein A (OspA) borreliacidal antibody by rIFN-gamma was not affected by the time of treatment. In addition, treatment with rIFN-gamma inhibited the production of other anti-B. burgdorferi antibodies. By contrast, treatment of cultures of immune lymph node cells with anti-IFN-gamma marginally increased the production of borreliacidal antibody and enhanced the production of other antibodies directed against B. burgdorferi. These results show that IFN-gamma does not play a major role in the production of anti-OspA borreliacidal antibody. Additional studies are needed to determine which cytokine(s) will enhance production of borreliacidal antibody.

Impaired NK cell development in an IFN-gamma transgenic mouse: aberrantly expressed IFN-gamma enhances hematopoietic stem cell apoptosis and affects NK cell differentiation

Aberrant expression of IFN-gamma has been demonstrated to cause a wide variety of alterations in cell function and development. Previously we reported that constitutive expression of IFN-gamma in bone marrow (BM) and thymus results in a total absence of B cells and a substantial decrease in the number of hematopoietic progenitor cells. In this study, we demonstrate a severe deficiency of NK1.1(+)CD3(-) cells in this transgenic mouse model. Compared with normal control littermates, we found a pronounced reduction of NK cells in IFN-gamma transgenic mouse spleen and liver despite maintenance of normal function. In addition, we observed a reduced number of BM cells in the IFN-gamma transgenic mouse despite normal expression of hematopoietic growth factors in the BM. Interestingly, these cells were less responsive to stem cell factor (SCF) despite c-kit expression on hematopoietic stem cells (HSCs). We observed that addition of exogenous IFN-gamma inhibited proliferation of HSCs and differentiation of NK precursors from HSCs in normal mice in response to SCF, IL-7, fms-like tyrosine kinase 3 ligand, and IL-15. Furthermore, we found that HSCs express the IFN-gammaRalpha subunit and undergo apoptosis in response to exogenous IFN-gamma. Thus, we have demonstrated the occurrence of a severe deficiency of NK cells and lower numbers of BM cells in an IFN-gamma transgenic mouse model. Furthermore, because exogenous IFN-gamma affects the responsiveness to hematopoietic growth factors such as SCF in vitro, our results indicate that chronic expression of IFN-gamma in vivo leads to widespread immune system defects, including alterations in NK cell differentiation.

Genes expressed during the IFN gamma-induced maturation of pre-B cells

Interferon-gamma (IFN gamma) exerts diverse responses in B cell development ranging from growth arrest and apoptosis to proliferation and differentiation. IFN gamma stimulates murine 70Z/3 pre-B cells to express surface immunoglobulin (Ig) and this system serves as a useful model for the pre-B to immature B cell transition in B cell development. To analyze this developmental transition, we used a PCR-based subtractive hybridization in combination with miniarray screening to identify differentially-expressed genes in IFN gamma-stimulated compared with unstimulated 70Z/3 pre-B cells. The majority (44%) of the differentially-expressed genes obtained were known IFN gamma-inducible. These included multiple isolates from each of three multi-gene families, including two guanylate-binding protein (47 and 67kDa GBP) families of GTPases and the hematopoietic IFN gamma-inducible nuclear protein family (HIN-200). These multiple isolates of genes comprised the majority of the total isolated and sequenced clones. Other known IFN gamma-induced genes in this group included Ig kappa light chain and Ly-6, as well as genes with functions in antigen processing, cellular regulation, and cytoskeletal organization. Another 36% of the genes identified were previously known, but not known to be IFN gamma-inducible (e.g. pre-B cell enhancing factor, PBEF). The remaining 20% of the IFN gamma-induced isolates did not match entries in Genbank, and thus, may represent novel genes involved in IFN gamma responses and/or in the pre-B to immature B cell transition. Overall, the majority of the individual genes isolated were either not known to be IFN gamma responsive or were not previously known.

Type I interferons and limitin: a comparison of structures, receptors, and functions

The type I interferon (IFN) family includes IFN-alpha, IFN-beta, IFN-pi, and IFN-tau. These molecules are clustered according to sequence homologies, use of the same cell surface receptor, and similar functions. IFN-alpha and IFN-beta have a globular structure composed of five a-helices. Their receptors, IFNAR1 and IFNAR2, belong to the class II cytokine receptor family for a-helical cytokines. Information about structure-function relationships between these and other IFNs is being provided by comparative sequence analysis, reference to a prototypic three-dimensional structure, analysis with monoclonal antibodies, construction of hybrid molecules and site directed mutagenesis. While much remains to be done, it should someday be possible to understand differences among IFNs in terms of how they interact with their corresponding receptors. Our recently identified IFN-like molecule, limitin, has weak sequence homology to IFN-alpha, IFN-beta, and IFN-omega and displays its biological functions through the same IFN-alpha/beta receptors. While limitin has antiproliferative, immunomodulatory, and antiviral effects like IFN-alpha and IFN-beta, it is unique in lacking influence on myeloid and erythroid progenitors. Further analysis of this functionally unique cytokine should be informative about complex IFN-receptor interactions. Furthermore, a human homologue or synthetic variant might be superior for clinical applications as an IFN without myelosuppressive properties.

Constitutive CD27/CD70 interaction induces expansion of effector-type T cells and results in IFNgamma-mediated B cell depletion

The interaction between the TNF receptor family member CD27 and its ligand CD70 provides a costimulatory signal for T cell expansion. Normally, tightly regulated expression of CD70 ensures the transient availability of this costimulatory signal. Mice expressing constitutive CD70 on B cells had higher peripheral T cell numbers that showed increased differentiation toward effector-type T cells. B cell numbers in CD70 transgenic (TG) mice progressively decreased in primary and secondary lymphoid organs. This B cell depletion was caused by CD27-induced production of IFNgamma in T cells. We conclude that apart from its role in controlling the size of the activated T cell pool, CD27 ligation contributes to immunity by facilitating effector T cell differentiation.

IFN-gamma induces the apoptosis of WEHI 279 and normal pre-B cell lines by expressing direct inhibitor of apoptosis protein binding protein with low pI

Interferon-gamma plays a crucial role in induction of Th1 response but is predominantly a negative regulator of B cell differentiation and Th2 response, so it is a key molecule in determining cellular or humoral immunity. In this study, we demonstrate that IFN-gamma induces apoptosis in WEHI 279 mouse B cells and IL-7-dependent mouse pre-B cells by disrupting mitochondrial membrane potential and cytochrome c release via down-regulation of Bcl-2 and Bcl-x(L). Furthermore, this apoptotic signal is promoted by the de novo synthesis of endogenous direct inhibitor of apoptosis protein binding protein with low pI (DIABLO) by IFN-gamma and its release from mitochondria into the cytosol. Inhibition of DIABLO expression by antisense oligonucleotide is sufficient to decrease caspase activities and DNA fragmentation, but not cytochrome c release from mitochondria, suggesting that DIABLO plays a critical role in promoting apoptotic signals downstream of mitochondrial events. Thus, these findings demonstrate a signaling pathway during B cell apoptosis induced by IFN-gamma and possible mechanisms by which B cell differentiation is negatively regulated by Th1-type cytokines.

High level class II trans-activator induction does not occur with transient activation of the IFN-gamma signaling pathway

Gene activation in early development is highly dependent on precise concentrations of trans-acting factors for the activation of different genes at differing points in the embryo. Thus, not only is the presence or absence of a particular trans-activator or repressor relevant in determining gene activation, but also the concentration of the regulatory protein must be above or below a certain threshold for proper gene regulation. Signaling pathways in somatic cells are thought to represent cascades of on/off switches, mediated most commonly by phosphorylation. Here we demonstrate a quantitative mechanism for regulating the level of a component of the IFN-gamma signaling pathway that in effect represents the differential sensitivities of STAT1, IFN-regulatory factor-1, and class II trans-activator (CIITA) to IFN-gamma. Unlike developmental gene regulation, in which specificity of gene activation is a function of regulatory protein concentrations, specificity of gene activation in the IFN-gamma signaling pathway is regulated by the duration of the activation of the primary IFN-gamma-regulatory protein, STAT1. This result most likely explains previously reported data indicating that a minimum amount of IFN-gamma is required for MHC class II gene activation despite the fact that the level of the IFN-gamma-inducible factor directly required for MHC class II induction, CIITA, directly correlates with the level of MHC class II expression. The induction of a high level of CIITA is dependent on sustained IFN-gamma signaling. The possible implications of this result for tumorigenesis are discussed.

Immunization and infection change the number of recombination activating gene (RAG)-expressing B cells in the periphery by altering immature lymphocyte production

Recombination activating gene (RAG) expression in peripheral B cells increases after immunization with (4-hydroxy-3-nitrophenyl) acetyl coupled to chicken gamma globulin (NP-CGG) in alum. This increase could result from reinduction of RAG expression or, alternatively, from accumulation of RAG-expressing immature B cells in the periphery. We have used mice that carry a green fluorescent protein (GFP) RAG indicator transgene (RAG2-GFP) to characterize the RAG-expressing B cells in immunized spleens. Most of the RAG2-GFP-expressing B cells in unimmunized spleen are immature B cells. Injection with NP-CGG in alum initially suppresses lymphopoiesis in the bone marrow and decreases the number of immature RAG2-GFP-expressing B cells in the spleen. Recovery of lymphopoiesis in the bone marrow coincides with accumulation of RAG-expressing immature B cells in the spleen. Most of the RAG-expressing cells that accumulate in the spleen after immunization do not proliferate and they are not germinal center cells. Neither the initial suppression of lymphopoiesis nor the subsequent accumulation of RAG-expressing cells in the spleen is antigen dependent, since similar changes are seen with alum alone. Furthermore, such changes in the numbers of developing and circulating immature lymphoid cells are seen after injection with complete Freund's adjuvant or malaria infection. Our experiments suggest that adjuvants and infectious agents cause previously unappreciated alterations in lymphopoiesis resulting in the accumulation of RAG-expressing immature B cells in the spleen.

Limitin: An interferon-like cytokine that preferentially influences B-lymphocyte precursors

We have identified an interferon-like cytokine, limitin, on the basis of its ability to arrest the growth of or kill lympho-hematopoietic cells. Limitin strongly inhibited B lymphopoiesis in vitro and in vivo but had little influence on either myelopoiesis or erythropoiesis. Because limitin uses the interferon alpha/beta receptors and induces interferon regulatory factor-1, it may represent a previously unknown type I interferon prototype. However, preferential B-lineage growth inhibition and activation of Janus kinase 2 in a myelomonocytic leukemia line have not been described for previously known interferons.

Interferon gamma induces the expression of p21waf-1 and arrests macrophage cell cycle, preventing induction of apoptosis

Incubation of bone marrow macrophages with lipopolysaccharide (LPS) or interferon gamma (IFN gamma) blocks macrophage proliferation. LPS treatment or M-CSF withdrawal arrests the cell cycle at early G1 and induces apoptosis. Treatment of macrophages with IFN gamma stops the cell cycle later, at the G1/S boundary, induces p21Waf1, and does not induce apoptosis. Moreover, pretreatment of macrophages with IFN gamma protects from apoptosis induced by several stimuli. Inhibition of p21Waf1 with antisense oligonucleotides or using KO mice shows that the induction of p21Waf1 by IFN gamma mediates this protection. Thus, IFN gamma makes macrophages unresponsive to apoptotic stimuli by inducing p21Waf1 and arresting the cell cycle at the G1/S boundary. Therefore, the cells of the innate immune system could only survive while they were functionally active.

RT1-U: Identification of a Novel, Active, Class Ib Alloantigen of the Rat MHC

In common with other mammalian species, the laboratory rat (Rattus norvegicus) expresses MHC class I molecules that have been categorized as either classical (class Ia) or nonclassical (class Ib). This distinction separates the class Ia molecules that play a conventional role in peptide Ag presentation to CD8 T cells from the others, whose function is unconventional or undefined. The class Ia molecules are encoded by the RT1-A region of the rat MHC, while the RT1-C/E/M region encodes up to 60 other class I genes or gene fragments, a number of which are known to be expressed (or to be expressible). Here we report upon novel MHC class Ib genes of the rat that we have expression cloned using new monoclonal alloantibodies and which we term RT1-U. The products detected by these Abs were readily identifiable by two-dimensional analysis of immunoprecipitates and were shown to be distinct from the class Ia products. Cellular studies of these molecules indicate that they function efficiently as targets for cytotoxic killing by appropriately raised polyclonal alloreactive CTL populations. The sequences of these class Ib genes group together in phylogenetic analysis, suggesting a unique locus or family. The combined serological, CTL, and sequence data all indicate that these products are genetically polymorphic.

How cells respond to interferons

Interferons play key roles in mediating antiviral and antigrowth responses and in modulating immune response. The main signaling pathways are rapid and direct. They involve tyrosine phosphorylation and activation of signal transducers and activators of transcription factors by Janus tyrosine kinases at the cell membrane, followed by release of signal transducers and activators of transcription and their migration to the nucleus, where they induce the expression of the many gene products that determine the responses. Ancillary pathways are also activated by the interferons, but their effects on cell physiology are less clear. The Janus kinases and signal transducers and activators of transcription, and many of the interferon-induced proteins, play important alternative roles in cells, raising interesting questions as to how the responses to the interferons intersect with more general aspects of cellular physiology and how the specificity of cytokine responses is maintained.

The Evolution of B Precursor Leukemia in the Eμ-ret Mouse

Eμ-ret mice carrying an RFP/RET fusion gene under the transcriptional control of the immunoglobulin heavy chain enhancer develop B lineage leukemias/lymphomas. We have characterized B-cell development in these mice before the onset of clinical disease to determine the steps involved in leukemogenesis. Flow cytometry reveals that the CD45R+CD43+CD24+BP-1+late pro–B-cell population is markedly expanded in the bone marrow of 3- to 5-week-old Eμ-ret mice. Compared with late pro–B cells from transgene-negative mice, Eμ-ret late pro–B cells have a limited capacity to differentiate in interleukin (IL)-7 and a higher incidence of VDJ rearrangements, but a similar cell cycle profile. In contrast, CD45R+CD43+CD24+BP-1−early pro–B cells from 3- to 5-week-old Eμ-ret mice, which also express the RFP/RET transgene, differentiate in IL-7 similarly to their normal counterparts. Furthermore, early pro–B cells from Eμ-ret and transgene-negative mice have an identical pattern of growth inhibition when exposed to interferons (IFNs)-α/β and -γ, whereas, pro–B-cell leukemia lines derived from Eμ-ret mice are markedly less sensitive to growth inhibition by these IFNs. In 13-week-old well-appearing Eμ-ret mice, late pro–B cells upregulate CYCLIN D1 expression and downregulate CASPASE-1 expression in a pattern that correlates with the emergence of B precursor cells in the peripheral blood and the loss of other B lineage subsets in the bone marrow. Taken together, these results suggest that the expression of the RFP/RET transgene initially prevents the normal elimination of late pro–B cells with nonproductive rearrangements. Secondary events that simultaneously disturb the normal transcriptional regulation of genes involved in the control of the cell cycle and apoptosis may allow for subsequent malignant transformation within the expanded late pro–B-cell population.

Interferon-gamma-induced differentiation and apoptosis of HT29 cells: dissociation of (glucosyl)ceramide signaling

Recently, (glyco)sphingolipids (SL) like ceramide (Cer) and glucosylceramide (GlcCer) have been shown to be involved in signaling pathways leading to differentiation and apoptosis in several cell types, including the colon adenocarcinoma cell line HT29. Intracellular levels of Cer can be modulated by ligands such as interferon-gamma (IFN gamma). In the present study we show that IFN gamma, depending on its concentration, has both differentiation- and apoptosis-inducing effects on HT29 cells. Since both phenomena have been related to SL-mediated signaling in other cell types, we next examined whether IFN gamma was able to induce changes in the SL levels of HT29 cells. Remarkably, no significant changes in these levels could be revealed, implying that SL are not involved in IFN gamma-induced differentiation and/or apoptosis of HT29 cells. This observation provides evidence for the hypothesis that SL-mediated signaling pathways might be more cell type specific than is generally assumed.

Vaccinia virus E3L protein is an inhibitor of the interferon (i.f.n.)-induced 2-5A synthetase enzyme

Induction of apoptosis in mammalian cells by double-stranded (ds) RNA-dependent enzymes, protein kinase (PKR), and 2-5A-synthetase/RNase L (referred to as the 2-5A system) might be a mechanism mediating anticellular and antiviral actions of interferon (i.f.n.). To counteract the effect of i.f.n., animal viruses have acquired genes that block specific i.f.n. pathways. Among poxviruses, vaccinia virus (VV) encodes E3L, a dsRNA-binding protein, which inhibits activation of i.f.n.-induced PKR. It has been proposed that E3L might also block activation of the 2-5A system, but direct proof is lacking. To establish if E3L inhibits the 2-5A system, we have developed a method to assay apoptosis induced by increased production of enzymes in the 2-5A pathway, as well as of their putative modulators. This assay is based on the use of cells derived from homozygous PKR knockout mice (Pkr-/-) infected with a VV mutant lacking E3L (delta E3L) and transiently transfected with a luciferase reporter gene together with plasmid vectors expressing 2-5A-synthetase, RNase L, or E3L, all controlled by the same inducible promoter. We found that expression of 2-5A-synthetase inhibited luciferase activity in a dose-response manner, reaching inhibition values of 80% relative to transfections with control plasmids. Similar results were obtained by transfection with an RNase L vector, although in this case the extent of inhibition was further enhanced upon coexpression of 2-5A-synthetase and RNase L. Inhibition of protein synthesis mediated by the 2-5A system correlated well with induction of apoptosis. Transfection of cells with a plasmid vector expressing E3L together with 2-5A-synthetase completely prevented apoptosis induced by this enzyme. We conclude that VV E3L acts as an inhibitor of the i.f.n.-induced 2-5A-synthetase enzyme.

Endogenous activation of apoptosis in bursal lymphocytes: inhibition by phorbol esters and protein synthesis inhibitors

The bursa of Fabricius represents the primary immune organ where immature B cells undergo maturational changes in avian species. Isolation of bursal lymphocytes for analysis in cell culture results in the rapid endogenous activation of apoptosis. After 2 h of incubation, over 45% of the lymphocytes were shown to be undergoing apoptosis and by 6 h 80% were undergoing apoptosis as demonstrated by a terminal deoxynucleotidyltransferase-mediated dUTP-fluorescein isothiocynate nick end-labeling flow-cytometric analysis. These results were corroborated by a propidium iodide-staining flow-cytometric assay and by an agarose gel electrophoresis DNA fragmentation assay that demonstrated internucleosomal DNA cleavage of genomic DNA in apoptotic bursal lymphocytes. Endogenous activation of apoptosis in bursal lymphocytes could be inhibited in a dose-dependent fashion with the phorbol ester, phorbol 12-myristate 13-acetate, but not the phorbol ester antagonist 4 alpha-phorbol 12,13-didecanoate. In addition, apoptosis could be inhibited in a dose-dependent fashion with inhibitors of protein translation, cycloheximide, and puromycin, as well as the transcriptional inhibitor actinomycin D. These results suggest that endogenous activation of bursal lymphocyte apoptosis may be mediated by the protein kinase C signal transduction pathway and activation of this process appears to be dependent upon de novo protein biosynthesis.

Fas Ligand Is Present in Human Erythroid Colony-Forming Cells and Interacts With Fas Induced by Interferon γ to Produce Erythroid Cell Apoptosis

Interferon γ (IFNγ) inhibits the growth and differentiation of highly purified human erythroid colony-forming cells (ECFCs) and induces erythroblast apoptosis. These effects are dose- and time-dependent. Because the cell surface receptor known as Fas (APO-1; CD95) triggers programmed cell death after activation by its ligand and because incubation of human ECFCs with IFNγ produces apoptosis, we have investigated the expression and function of Fas and Fas ligand (FasL) in highly purified human ECFCs before and after incubation with IFNγ in vitro. Only a small percentage of normal human ECFCs express Fas and this is present at a low level as detected by Northern blotting for the Fas mRNA and flow cytometric analysis of Fas protein using a specific mouse monoclonal antibody. The addition of IFNγ markedly increased the percentage of cells expressing Fas on the surface of the ECFCs as well as the intensity of Fas expression. Fas mRNA was increased by 6 hours, whereas Fas antigen on the cell surface increased by 24 hours, with a plateau at 72 hours. This increase correlated with the inhibitory effect of IFNγ on ECFC proliferation. CH-11 anti-Fas antibody, which mimics the action of the natural FasL, greatly enhanced IFNγ-mediated suppression of cell growth and production of apoptosis, indicating that Fas is functional. Expression of FasL was also demonstrated in normal ECFCs by reverse transcriptase-polymerase chain reaction and flow cytometric analysis with specific monoclonal antibody. FasL was constitutively expressed among erythroid progenitors as they matured from day 5 to day 8 and IFNγ treatment did not change this expression. Apoptosis induced by IFNγ was greatly reduced by the NOK-2 antihuman FasL antibody and an engineered soluble FasL receptor, Fas-Fc, suggesting that Fas-FasL interactions among the ECFCs produce the erythroid inhibitory effects and apoptosis initiated by IFNγ.

Impairment of T and B cell development by treatment with a type I interferon

Type I interferons alpha and beta, naturally produced regulators of cell growth and differentiation, have been shown to inhibit IL-7-induced growth and survival of B cell precursors in vitro. After confirming an inhibitory effect on B lymphopoiesis in an ex vivo assay, we treated newborn mice with an active IFN-alpha2/alpha1 hybrid molecule to assess its potential for regulating B and T cell development in vivo. Bone marrow and splenic cellularity was greatly reduced in the IFN-alpha2/alpha1-treated mice, and B lineage cells were reduced by >80%. The bone marrow progenitor population of CD43+B220+HSA- cells was unaffected, but development of the CD19+ pro-B cells and their B lineage progeny was severely impaired. Correspondingly, IL-7-responsive cells in the bone marrow were virtually eliminated by the interferon treatment. Thymus cellularity was also reduced by >80% in the treated mice. Phenotypic analysis of the residual thymocytes indicated that the inhibitory effect was exerted during the pro-T cell stage in differentiation. In IFN-alpha/beta receptor-/- mice, T and B cell development were unaffected by the IFN-alpha2/alpha1 treatment. The data suggest that type I interferons can reversibly inhibit early T and B cell development by opposing the essential IL-7 response.

Activation of the IFN-inducible enzyme RNase L causes apoptosis of animal cells

The interferon (IFN)-induced enzyme RNase L produced by a recombinant vaccinia virus (VV) causes death of mammalian cells with morphological and biochemical characteristics of apoptosis. Coexpression of 2-5A-synthetase enhances apoptosis induced by RNase L Activation of endogenous RNase L by infection with a VV ts mutant (ts22) or with wild-type virus in the presence of the antipoxvirus drug isatin-beta-thiosemicarbazone, a treatment known to significantly increase the amount of double-stranded RNA late during infection, also causes pronounced apoptosis of infected cells. The effects observed with recombinant virus-derived RNase L or with the endogenous enzyme are specific, since apoptosis also occurs in cells derived from mice lacking the IFN-induced protein kinase (PKR). The apoptosis antagonist Bcl-2 prevents induction of cell death by RNase L activation. Apoptosis of mammalian cells by RNase L activation could be a mechanism mediating anticellular actions of IFN.

Apoptosis of myelin-reactive T cells induced by reactive oxygen and nitrogen intermediates in vitro

Apoptosis is a major mechanism of T cell elimination during ontogeny and tolerance induction as well as in autoimmunity. To assess the possible involvement of reactive oxygen and nitrogen intermediates (ROI and NO.) in T-cell apoptosis during autoimmune demyelination we investigated the effects of H2O2 and NO. in vitro on activated autoreactive CD4+ T cell lines capable of transferring experimental autoimmune encephalomyelitis (EAE) and experimental autoimmune neuritis (EAN). For detection and quantitation of apoptotic cells, DNA fragmentation was assessed by in situ tailing with fluorescein-ddUTP and subsequent flow cytometric analysis. H2O2 applied directly to the cell cultures for 6 to 18 hr at concentrations of 10 to 300 microM and ROI released by combination of hypoxanthine and xanthine oxidase (HX/XO) caused apoptosis in a dose-dependent manner in 13-33% of T cells of neuritogenic and encephalitogenic T cell lines. Apoptosis induction could be suppressed by the H2O2-neutralizing enzyme catalase. NO. released by the penicillamine derivative SNAP induced apoptosis to a similar extent as ROI. Maximum values were 38% in an encephalitogenic V beta 8.2-T cell receptor-bearing T cell line and 26% in a neuritogenic T cell line. T cell lines with specificity to ovalbumin revealed slightly lower susceptibility to apoptosis induction by all three kinds of trigger, which is, however, most probably not due to the different antigen specificity, but rather a result of fewer in vitro restimulation cycles of these cells. In neuritogenic cells high-dose (100 units/ml) exogenous interleukin-2 (IL-2) prevents H2O2-induced apoptosis. In conclusion, macrophage-derived reactive oxygen and nitrogen intermediates have the potency to limit inflammatory demyelination by elimination of autoreactive and bystander T cells via apoptotic cell death, and IL-2 is a rescue factor.

A transgenic marker for mouse B lymphoid precursors

Three lines of transgenic mice have been generated which express human CD25 under the control of the 722-base pair region located immediately 5' of the precursor (pre)-B cell-specific lambda5 gene. All three strains express human CD25 in parallel to endogenous lambda5 on pre-B cells, but not on mature B lymphocytes or other blood cell lineages. High expression of human CD25 on B lineage cells of transgenic mice has allowed the identification of a new B220+CD19-lambda5+ precursor of the B220+CD19+lambda5+ c-kit+ pre-BI cells. Both types of precursors are clonable on stromal cells in the presence of interleukin-7. The CD19- precursors have a sizeable part of their immunoglobulin heavy chain gene loci in germline configuration, while the CD19+ pre-BI cells are predominantly DJH rearranged. The results indicate that random integration of the 722-bp 5' region of the lambda5 gene into the mouse genome confers tissue and differentiation stage-specific expression of a transgene.

Bone Marrow and Thymus Expression of Interferon-γ Results in Severe B-Cell Lineage Reduction, T-Cell Lineage Alterations, and Hematopoietic Progenitor Deficiencies

Interferon-γ (IFN-γ) is an immunoregulatory lymphokine that is primarily produced by T cells and natural killer cells. It has effects on T-cell, B-cell, and macrophage differentiation and maturation. We have developed transgenic mice that express elevated levels of IFN-γ mRNA and protein by inserting multiple copies of murine IFN-γ genomic DNA containing an Ig λ-chain enhancer in the first intron. The founder line carrying eight copies of this transgene has eightfold to 15-fold more IFN-γ–producing cells in the bone marrow and spleen than do nontransgenic littermates. Transgenic mice show a pronounced reduction in B-lineage cells in the bone marrow, spleen, and lymph nodes. In addition, single positive (CD4+,CD8− and CD4−,CD8+) thymocyte numbers are increased twofold, yet the number of splenic T cells is reduced by 50%. There is also a twofold to threefold decrease in the frequency and total number of myeloid progenitors in the bone marrow. Granulomatous lesions and residual degenerating cartilaginous masses are also present in the bones of these mice. Overall, our data show that the abnormal expression of IFN-γ in these transgenic mice results in multiple alterations in the immune system. These animals provide an important model to examine the role of IFN-γ expression on lymphoid and myeloid differentiation and function.

The SCID but not the RAG-2 gene product is required for S mu-S epsilon heavy chain class switching

We have investigated the capacity of precursor B cells from normal (BDF1) and V(D)J recombinase-deficient (RAG-27) or defective (SCID) mice to be induced by a CD40-specific monoclonal antibody and IL-4 to epsilon H chain gene transcription and to S mu-S epsilon switch recombination. In differentiating precursor B cells from all three strains of mice, the development of similar numbers of CD19+, CD23+, CD40+, and MHC class II+ expressing B lineage cells and similar levels of epsilon H chain gene transcription were induced. Efficient S mu-S epsilon switching occurred in normal and RAG-2-deficient, but not in SCID, precursor B cells. Thus, the transcription of the epsilon H chain is independent of the RAG-2 and the SCID gene product, while the S mu-S epsilon switch recombination requires the SCID gene-encoded DNA-dependent protein kinase, but not the RAG-2 protein.

Interferon-gamma in autoimmunity

Autoimmune disorders are characterized by abrogation of self-tolerance, resulting in emergence of activated self-reactive lymphocyte clones that trigger or maintain inflammatory reactions in specific organs. Interferon-gamma (IFN-gamma), as well as other cytokines, plays an important role as a regulator of the activation of self-reactive lymphocytes and of bystander and accessory cells that are involved in the autoimmune inflammatory response. In experimental models of autoimmunity, endogenous IFN-gamma has invariably been found to profoundly affect the disease course. However, it acts in one way in some diseases and in the opposite way in others.